Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from wind using known foil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
To ensure that wind power remains a viable energy source, efforts have been made to increase energy outputs by modifying the size and capacity of wind turbines, including increasing the length and surface area of the rotor blades. However, the magnitude of deflection forces and loading of a rotor blade is generally a function of blade length, along with wind speed, turbine operating states, blade stiffness, and other variables. This increased loading not only produces fatigue on the rotor blades and other wind turbine components, but may also increase the risk of a sudden catastrophic failure of the rotor blades, for example when excess loading causes deflection of a blade resulting in a tower strike.
Load control is thus a crucial consideration in operation of modern wind turbines. Active pitch control systems are widely used to control the load on the rotor blades by varying the pitch of the blades. However, in high wind conditions, it is often difficult to adjust the pitch angle of the blades due to increased wind resistance and the response rate of the pitch control system.
It is also known to vary the aerodynamic characteristics of the individual rotor blades as a means of load control, for example with controllable vortex elements (“generators”), flaps, tabs, and the like configured on the blade surfaces.
U.S. Pat. No. 6,984,110 describes a system wherein the windmill blades are provided with wind pressure adjusting holes that are variably covered by adjustable plates configured on a side of the blade so as to slide within guides along the surface of the blade. A relatively complex mechanical actuating and control system is required to simultaneously adjust all of the plates on a single blade.
U.S. Pat. No. 7,400,057 describes an omni-directional vertically oriented wind turbine with toroid stacked blades. The blades include air bleed channels along the leading edge and concave surface of each toroid for the purpose of introducing high kinetic energy from the leading edge to the convex surface of the blade to reinforce the boundary layer and reduce airflow separation along the blade. These channels are open (uncovered) and play no meaningful role in load control on the blades.
Accordingly, the industry would benefit from a load control system and method for individual rotor blades that does not adversely affect the aerodynamic performance of the blade within design load constraints and is relatively easy to actuate under high load conditions.